A significant factor in the fabrication of aircraft structures is the cost encountered in preparing holes to accept the wide variety of fasteners used. The large number of holes involved (250,000 to 400,000 for a fighter aircraft and 1 or 2 million for bomber and transport aircraft) means that this manufacturing task has become a major production cost area. Over the past 20 years, major improvements have been made in automating various processes in the aerospace industry. Drilling of subassemblies can be accomplished with automatic drilling and riveting equipment which can drastically reduce manufacturing costs. Unfortunately, a major portion of the drilling must be performed in assembly fixtures on the production floor. These drilling operations are still performed manually because the equipment and controls to realize the potential economic benefits of an automated system have not yet been developed. The system must be capable of operating in five axes of motion to drill contoured skins of the aircraft structure and be able to automatically adjust for the minor variations in understructure positioning.
The concept of an automated assembly fixture drilling system is truly generic. Such a system would be able to reduce manufacturing costs on composite and metal structures, large and small aircraft and rebuilding facilities.
The most apparent approach to the problem of automating assembly drilling operations would be to build a multi-axis numerically controlled or computer controlled drilling work station. However, this has been found to be a superficial answer for aircraft structure drilling since it in itself would not compensate for variations in actual structure position. It would require a complex programing system and become a major piece of capital equipment which would be severely under utilized since there are many non-drilling operations required in such an assembly fixture. These factors coupled with the trend in recent years for aircraft to become more sophisticated with hundreds of thousands of holes and relatively low production rates has economically eliminated the practicality of such specialized high cost equipment.
A major obstacle to the automation of aircraft structure assembly fabrication in the past has been an inability to recognize that minor structure position variations occur on the assembly floor for which the mechanic makes the necessary tooling adjustments to maintain proper edge distance. An automated drilling assembly with a conventional gimbaled drive system is unsatisfactory since it is costly, fragile and difficult to hold in proper position.